In case you didn't know (and honestly, why would you?), Nov. 19 is World Toilet Day  an event hosted by the World Toilet Organization to raise awareness for the 2.5 billion people around the world who live without proper sanitation. But even for those of us with access to modern plumbing, how often do we really think about our toilets? From outhouses to water closets  even former Merrill Lynch CEO John Thain's $35,000 "commode on legs" (technically a table, not a toilet)  humans have been devising creative ways to go to the bathroom since, well, the first person crossed his legs with an urgent need to go. (See the top 10 environmental ideas.)

It's unclear who first invented the toilet. Early contenders for the honor are the Scots and the Greeks. Skara Brae, a Neolithic settlement on the Scottish mainland dating back to 3,000 B.C., features stone huts equipped with drains extending from recesses in their walls  a feature that historians believe were for residents' bathroom needs. The Palace of Knossos on Crete, built around 1,700 B.C., features definite latrines: large, earthenware pans connected to a water supply that ran through terra-cotta pipes. Europeans had nothing of comparable sophistication until well into the 16th century.

Ancient Rome is famous for its public bathhouses  the Baths of Caracalla are six times larger than St. Paul's Cathedral and could serve 1,600 people at once  and the Roman commitment to hygiene didn't stop with just bathing. At one point Rome boasted 144 communal lavatories. The city's giant toilets, with their long, benchlike seats, were not used every day; for the most part, Romans threw their waste onto the streets.

Medieval England wins the gross-out award for its invention of the castle garderobe  a protruding room with a tiny opening out of which royalty would do their business. The garderobe was usually suspended over a moat that collected all manner of human discards, making for a particularly uninviting hurdle for an invading army. Peasants and serfs relieved themselves in communal privies located at the end of their streets, or in the case of those living along the London Bridge, right into the River Thames.

Garderobes and public toilets were eventually replaced with something slightly more recognizable to the modern-day defecator: a box with a lid. France's Louis XI hid his toilet behind curtains and used herbs to keep his bathroom scented; England's Elizabeth I covered her commode in crimson velvet bound with lace.

In 1596, England lept into modern sanitation when Sir John Harrington, godson of Elizabeth I, published Metamorphosis of Ajax, in which he described a new kind of water closet: a raised cistern with a small pipe down which water ran when released by a valve. The Queen installed Harrington's invention in her palace at Richmond, but it took another 200 years before a man named Alexander Cummings developed the S-shaped pipe underneath the basin to keep out foul odors. At the end of the 18th century, the flushable toilet went mainstream.

In the 1880s, England's Prince Edward (later to become King Edward VII) hired a prominent London plumber named Thomas Crapper to construct lavatories in several royal palaces. While Crapper patented a number of bathroom-related inventions, he did not  as is often believed  actually invent the modern toilet. He was, however, the first one to display his bathroom wares in a showroom, so that when customers needed a new fixture, they would immediately think of his name.

Bathroom technology really took off in the 20th century. Flushable valves, water tanks that rest on top of the bowl rather than above, toilet-paper rolls (invented in 1890 but not heavily marketed until 1902)  these minor improvements seem like necessities now. And if you think the toilet hasn't changed recently, think again: in 1994 Congress passed the Energy Policy Act, requiring common flush toilets to use only 1.6 gallons of water, less than half of what they consumed before. The "low flow" law left a lot of consumers dissatisfied (and a lot of toilets clogged) until companies developed better models, many of which  if we're lucky enough to be counted among the 60% of the world's population with access to proper sanitation  we use today.